fix(fastfetch): show only the product name on the Host line

[DevSecNinja]

Why

On OEM hardware the fastfetch Host line is mostly noise. fastfetch's default host format appends the product version, which on a Surface Laptop is a firmware/SKU string, so the line reads:

Host: Microsoft Surface Laptop, 7th Edition (124I:00108T:000M:0000000F:0B:10C:12M:04D:03U:04T:1R:21S:0A:0)

The useful part (the model name) gets pushed out of view by 60 characters that mean nothing to a human reading a login banner.

What changed

Replaces the bare "host" module in config.jsonc.tmpl with an explicit { "type": "host", "format": "{name}" }, giving:

Host: Microsoft Surface Laptop, 7th Edition

{name} is populated on Linux and macOS too (it is the DMI/SMBIOS product name), so this is not Windows specific and the module stays in the shared, non-templated part of the config.

Also adds a short note in docs/customization.md explaining the deviation from fastfetch's defaults, and a Pester assertion in the existing "fastfetch chezmoi wiring" block so the format is not silently dropped by a future edit.

Notes for reviewers

While looking into this, the Updates line was also missing from the banner. That turned out to be a stale cache from the source/rendered split in #654 rather than a code defect: the rendered updates file had no .src sibling yet, so it was cleaned up as an orphan while the refresh stamp was still fresh. A single status.ps1 refresh restored it, and hourly refreshes keep it correct from here, so no code change was needed for it.

Testing

• Invoke-Pester -Path tests\powershell\FastfetchStatus.Tests.ps1 (65 passed)
• Rendered the real banner locally after chezmoi apply to confirm the Host and Updates lines